In the past decade the portable electronics industry has made enormous technological strides. Today, portable electronics, such as cell phones, MP3 players, digital cameras, etc., offer a greater range of services and smaller sizes than ever before. A large reason for the advances that have occurred in the portable electronics sector has been advances in integrated chip memory.
Memory used in integrated chips can be broadly categorized into two main categories: non-volatile memory and volatile memory. Non-volatile memory is memory that does not require power to maintain its data. There are numerous types of non-volatile memories on the market including Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), and flash memory. In recent years flash memory has dominated the market of non-volatile memory. Flash memory has the ability to erase a single memory cell at a time and offers higher density and faster read times than other forms of non-volatile memory.
Volatile memory requires a constant power supply to maintain its data. From a performance point of view, volatile memory is superior to non-volatile memory, offering faster read and write speeds at higher density. The most commonly used volatile memories are static random access memory (SRAM) and dynamic random access memory (DRAM). SRAM offers high read speed and low power consumption, while DRAM offers high density memory at a low cost. In today's integrated chips, both SRAM and DRAM offer higher performance and larger density than ever before.
Unfortunately, to receive the higher performance of volatile memory over non-volatile memory it is necessary to increase the power consumption of the chip. In recent years, certain markets such as the high end cell phone market have looked to combine the advantages of volatile and non-volatile memories. They have developed memory architectures to take advantage of different memory properties within the same chip. For example, in the past few years it has become popular to combine non-volatile NAND-type flash memory with volatile random access memory (RAM). This combination provides the advantages of high density, low power non-volatile memory (NVM) of the NAND-type flash with the high performance, high density of volatile RAM memories. However, even this architecture fails to realize all the advantages of flash and RAM based memories.